Many systems require a wiring and/or electrical contacts in order to supply electrical power to devices. Omitting these wires and contacts provides for an improved user experience. Traditionally, this has been achieved using batteries located in the devices but this approach has a number of disadvantages including extra weight, bulk and the need to frequently replace or recharge the batteries. Recently, the approach of using wireless inductive power transfer has received increasing interest.
Part of this increased interest is due to the number and variety of portable and mobile devices having exploded in the last decade. For example, the use of mobile phones, tablets, media players etc. has become ubiquitous. Such devices are generally powered by internal batteries and the typical use scenario often requires recharging of batteries or direct wired powering of the device from an external power supply.
As mentioned, most present day devices require a wiring and/or explicit electrical contacts to be powered from an external power supply. However, this tends to be impractical and requires the user to physically insert connectors or otherwise establish a physical electrical contact. It also tends to be inconvenient to the user by introducing lengths of wire. Typically, power requirements also differ significantly, and currently most devices are provided with their own dedicated power supply resulting in a typical user having a large number of different power supplies with each power supply being dedicated to a specific device. Although, internal batteries may prevent the need for a wired connection to an external power supply, this approach only provides a partial solution as the batteries will need recharging (or replacing which is expensive). The use of batteries may also add substantially to the weight and potentially cost and size of the devices.
In order to provide a significantly improved user experience, it has been proposed to use a wireless power supply wherein power is inductively transferred from a transmitter coil in a power transmitter device to a receiver coil in the individual devices.
Power transmission via magnetic induction is a well-known concept, mostly applied in transformers which have a tight coupling between the primary transmitter coil and the secondary receiver coil. By separating the primary transmitter coil and the secondary receiver coil between two devices, wireless power transfer between the devices becomes possible based on the principle of a loosely coupled transformer.
Such an arrangement allows a wireless power transfer to the device without requiring any wires or physical electrical connections. Indeed, it may simply allow a device to be placed adjacent to, or on top of, the transmitter coil in order to be recharged or powered externally. For example, power transmitter devices may be arranged with a horizontal surface on which a device can simply be placed in order to be powered.
Furthermore, such wireless power transfer arrangements may advantageously be designed such that the power transmitter device can be used with a range of power receiver devices. In particular, a wireless power transfer approach known as the Qi Specification has been defined and is currently being developed further. This approach allows power transmitter devices that meet the Qi Specification to be used with power receiver devices that also meet the Qi Specification without these having to be from the same manufacturer or having to be dedicated to each other. The Qi Specification further includes some functionality for allowing the operation to be adapted to the specific power receiver device (e.g. dependent on the specific power drain).
The Qi Specification is developed by the Wireless Power Consortium and more information can e.g. be found on their website: http://www.wirelesspowerconsortium.com/index.html, where in particular the defined Specification documents can be found.
In order to support the interworking and interoperability of power transmitters and power receivers, it is preferable that these devices can communicate with each other, i.e. it is desirable if communication between the power transmitter and power receiver is supported, and preferably if communication is supported in both directions.
The Qi Specification supports communication from the power receiver to the power transmitter thereby enabling the power receiver to provide information that may allow the power transmitter to adapt to the specific power receiver. In the current Specification, a unidirectional communication link from the power receiver to the power transmitter has been defined and the approach is based on a philosophy of the power receiver being the controlling element. To prepare and control the power transfer between the power transmitter and the power receiver, the power receiver specifically communicates information to the power transmitter.
The Qi Specification is being developed to support increasingly high power demanding applications. For example, the Specification is intended to be used with devices consuming several kilowatts of power.
For example, the wireless power transfer is expected to increasingly be used with e.g. kitchen appliances such as kettles, blenders, food processors etc. In particular, wireless power transfer is envisaged to be used for providing power to various heating devices. For example, the concept is expected to be widely used e.g. in cooking stoves supporting kettles and pans that are heated by means of magnetic induction.
Indeed, it is envisaged that wireless power transfer may be used to provide flexible power in environments such as kitchens. In many scenarios, it is expected that the apparatus providing the wireless transfer may be designed to support both appliances that are used for heating as well as non-heating appliances. Accordingly, the apparatus providing the wireless transfer may be designed to e.g. have different areas or surfaces that have different thermal resistance. E.g., some areas may be designed to receive a heating element whereas other areas may be intended for non-heating appliances.
As a specific example, a kitchen apparatus for providing wireless power may provide a surface (such as a kitchen table top) having an area designed to power heating appliances, such as kettles and pans, and a second area designed to provide power to non-heating appliances, such as blenders or food processors. Accordingly, one area may be made from a material with a high thermal robustness, whereas another area may be made from a material which is vulnerable to high temperatures.
As an example, FIG. 1 illustrates an example of a wireless power provision to a non-heating appliance and FIG. 2 illustrates an example of a wireless power provision to a heating appliance (such as a pan or a kettle).
In the examples, the power providing apparatus comprises a power transmitter 101 which is shown as being sub-divided into a power source 103, a transmitter coil 105, and an inverter 107 receiving power from the power source 103 and generating a drive signal for the transmitter coil 105. The transmitter coil 105 is located close to or integrated within a kitchen worktop 109. A non-heating kitchen appliance 111 is positioned on the worktop in the example of FIG. 1 and a heating appliance 111, such as a kettle is positioned on the worktop in the example of FIG. 2. The heating appliance 111 of FIG. 2 has a heating element 201 in which the power transmitter 101 may induce eddy currents which result in the heating element heating up.
In the example, the worktop 109 may be divided into a cooking zone illustrated by FIG. 2 and a food preparation zone illustrated by FIG. 1. In the example, the cooking zone may comprise an induction cooking plate which heats e.g. a kettle or a pan by magnetic induction. The bottom of the pan or kettle may get very hot and the cooking zone may be arranged to withstand such temperatures. E.g., a ceramic cooking plate can withstand a temperature of 200 C.° or more.
Likewise, the preparation zone may comprise a power transmitter integrated in the worktop in order to power appliances. However, for this area, the material used is typically not resistant to high temperatures. For example, typical kitchen worktops may be made from materials such as wood or granite. However, these materials may have a much lower heat resistance and may be damaged if subjected to the high temperatures of the kettle.
Having both wireless power transmitters in the cooking zone and in the preparation zone may result in concerns about the expected user behavior. A user will expect a pan to become hot when it is on a cooking stove. However, he may also desire to use the power transmitter of the preparation zone for powering the heating appliance. However, this can result in damage to the worktop caused by the high temperatures. Indeed, many appliances that include heating are now perceived to belong more to the preparation zone than a cooking zone. For example, appliances such as toasters, water kettles, rice cookers, etc. are nowadays typically used on the kitchen worktop rather than on the stove. It is expected that the functions provided by the cooking zone and the preparation zone will continue to increasingly merge.
Thus, a potential problem arises if the power transmitter of the preparation zone generates an alternating magnetic flux field that may be received by a heating appliance, for instance a water kettle or a frying pan. This may cause the underside of the pan or kettle to become very hot (typically due to the generation of Eddy currents in the heating plate or element). The generated heat may result in damage to the worktop.
Furthermore, although the heating appliance may typically be arranged to control the temperature of the heating element, e.g. by controlling the power of the power transfer signal, a fault or error scenario could potentially result in undesirably high temperatures which could potentially result in damage to the surface. For example, temperature control using the power control loop to adjust the power of the power transfer signal requires reliable communication between the power receiver and the power transmitter. If communication errors occur, or indeed if the communication link is lost, the temperature may be unregulated and could result in temperatures that are too high. Such a scenario may occur if the power transmitter is positioned on a coaster or trivet in order to protect the surface. Such an arrangement will inherently result in an increased distance between the transmitter and receiver coils and this could result in an unreliable load modulation communication.
Undesirable temperatures could e.g. also result from faults occurring in the heating appliance. For example, a faulty temperature sensor could result in the temperature in a heating plate in which the power transfer signal induces eddy currents, and thus heating, always being measured below the target temperature. As a result, the power receiver will continue to request increased power from the power transmitter resulting in the temperature of the heating plate increasing beyond the desirable levels.
More generally, the increased flexibility and variation of applications of wireless power transfer at increasingly high power levels, where in particular the power transfer may support heated power consuming devices, has led to increased risks and complications. This may in particular be the case for kitchen scenarios using wireless power transfer but is not limited to such applications.
Hence, an improved wireless power transfer approach would be advantageous and in particular an approach allowing increased flexibility, reduced risk of damage, improved support for different applications and usage scenarios, additional safety and in particular additional or improved overheating protection, facilitated user operation and/or improved performance would be advantageous.